CN102340029A - A functional additive for non-aqueous electrolytes of lithium-ion batteries - Google Patents

Abstract

The invention discloses a functional additive for a non-aqueous electrolyte of a lithium-ion battery, the amount of which is equivalent to 0.01-5% of the mass of the electrolyte composed of carbonate solvent and lithium salt, more preferably 0.05-1.5% of the mass of the electrolyte %. Using the additive of the invention can effectively improve the high-temperature cycle performance of the lithium-ion battery, and at the same time increase the oxidation resistance of conventional carbonate electrolytes to 5.0V. The additive of the invention has low cost, remarkable effect and good application prospect.

Description

A functional additive for non-aqueous electrolytes of lithium-ion batteries

technical field

The invention relates to an electrolyte solution of a lithium ion battery, in particular to a functional additive for the electrolyte solution of a lithium ion battery for improving battery cycle performance and increasing electrolyte decomposition voltage.

Background technique

Lithium-ion batteries have become a research hotspot in the field of new energy due to their high operating voltage, high energy density and long cycle life. Currently used cathode materials for lithium-ion _batteries , such as LiCoO ₂ , _{LiMn 2} O ₄ and LiFePO _{4 ,} have working voltages lower than 4V _. The voltage can be as high as around 5V. However, the above-mentioned positive electrode materials will cause the dissolution of active metal ions due to the generation of HF or other acidic substances in the electrolyte during use, thereby seriously affecting the cycle performance of the battery. This phenomenon is particularly serious at high temperatures, J PowerSources (2004, 129: 14-19), J Electrochem Soc (2005, 152(6): A1041-A1046) and Flectrochem Communica (2005, 7: 669-673) and other documents have confirmed this point. In addition, the attenuation of high-voltage materials is also closely related to the composition of the electrolyte. The current conventional electrolyte system will decompose when the voltage is higher than 4.5V, resulting in a decrease in the performance of the entire battery system. J Power Sources (2001, 99: 60-65), J Power Sources (2009, 189(1): 685-688), Electrochem Solid-State Lett (2002, 5(9): A206-A208), J ElectrochemSoc (2005 , 152(7): A1361-A1365), J Power Sources (2007, 168: 258-264), J Power Sources (2003, 119-121: 378-382) and US5707760 and other literature research results show that LiBOB or LiB (C ₂ O ₄ ) ₂ can form a chelate complex with metal ions leached from the positive electrode, reducing the probability of metal ions being reduced to the negative electrode and improving battery cycle performance; using (CH ₃ ) ₃ SiNHSi(CH ₃ ) ₃ , pyridine, NH ₄ I and Additives such as dimethylacetamide can effectively improve the stability of the electrolyte, inhibit the formation of HF, reduce the dissolution of the positive electrode, and improve the cycle performance of the battery, especially the high-temperature cycle performance.

Contents of the invention

The primary purpose of the present invention is to improve the stability of LiPF ₆ in the electrolyte, and improve the cycle performance of the positive electrode material, especially the high-temperature cycle performance. The present invention proposes a functional additive that can improve the stability of LiPF ₆ and inhibit the generation of HF. The use of the additive can reduce the dissolution of positive metal ions, and at the same time, the additive can effectively chelate the dissolved metal ions, reducing the The possibility of ions being reduced at the negative electrode; in addition, the functional additive proposed by the present invention can effectively improve the stability of conventional carbonate electrolytes under high voltage.

The purpose of the present invention is achieved through the following technical solutions: add 0.01-5wt.% additives to the conventional lithium-ion battery carbonate common electrolyte, and mix evenly;

Described additive is 8-hydroxyquinoline (HQ);

The amount of the additive is more preferably 0.05-1.5% of the mass of the carbonate-based common electrolyte.

Invention principle of the present invention: 8-hydroxyquinoline is an organic compound with chelating function, which contains H ⁺ donor (-OH group) and acceptor (-N=group), which can be combined with H in the electrolyte ₂ O or HF forms a complex, reduces the generation of HF or reduces the transfer reaction of fluoride ions to solvent molecules, acts as an electrolyte stabilizer, and improves the antioxidant stability of the electrolyte; at the same time, 8-hydroxyquinoline has excellent chelating properties It can form chelates with metal ions that have been leached from the positive electrode, reducing the possibility of metal ions being reduced at the negative electrode, thereby improving the cycle performance of lithium-ion batteries.

Compared with the prior art, the present invention has the following advantages and effects:

(1) Using the lithium-ion battery functional electrolyte additive of the present invention can effectively improve the cycle performance of the lithium-ion battery, especially the high-temperature cycle performance, and can effectively increase the decomposition potential of the conventional electrolyte to 5.0V;

(2) The additive of the present invention is low in cost and has good application prospects.

Description of drawings

Fig. 1 is the cyclic voltammetry curve (scanning speed 0.2mV/s) of a kind of _LiFePO4 in embodiment 1 in ordinary electrolyte and electrolyte containing additives.

Fig. 2 is a descriptive test diagram (scanning speed 5mV/s) of the electrolyte solution and graphite negative electrode containing additives in Example 2.

Fig. 3 is the linear sweep voltammetry curve (scanning speed 5mV/s) of common electrolytic solution and the electrolytic solution containing additive in embodiment 4.

Figure 4 shows the cycle performance of charging and discharging at 60°C and 0.5C using a 10Ah square lithium iron phosphate battery containing an additive electrolyte in Example 5.

Detailed ways

The present invention will be described in further detail below in conjunction with the examples, but the embodiments of the present invention are not limited thereto.

Example 1

Prepare a basic electrolyte of 1M LiPF ₆ EC/EMC/DEC (1:1:1w), add 1.0wt% additive HQ to the basic electrolyte to make a new electrolyte, and test it with a three-electrode system on a CHI660D electrochemical workstation Compatibility of electrolyte with _LiFePO4 cathode. The working electrode was prepared by uniformly mixing the lithium iron phosphate sample, conductive carbon black and polytetrafluoroethylene at a mass ratio of 82:10:8, and the reference electrode and the counter electrode were metal lithium sheets. Figure 1 is the cyclic voltammogram of LiFePO ₄ in two electrolytes. It can be seen that the additive HQ does not affect the normal deintercalation of lithium ions in the electrode material.

Example 2

Mix graphite, binder and conductive agent in a ratio of 90:2:8 to make negative electrode slurry, evenly coat it on copper foil, and dry it at 80°C for 60 minutes to make lithium ion battery negative electrode sheet. The compatibility of 1M LiPF ₆ EC/EMC/DEC (1:1:1w) basic electrolyte containing additive HQ with graphite anode was tested with a three-electrode system on CHI660D electrochemical workstation. Figure 2 shows the cyclic voltammogram of the graphite negative electrode in the basic electrolyte containing 1 wt% additive HQ, indicating that the additive HQ has good compatibility with the graphite negative electrode.

Example 3

Add 0.5wt% additive HQ to 1M LiPF ₆ EC/EMC/DEC (1:1:1w) base electrolyte, then seal the electrolyte and place it in a vacuum drying oven in a vacuum glove box with a moisture content of less than 5ppm Inside, store at 45°C for 2 days, and investigate the changes of moisture and HF content in the electrolyte before and after high-temperature storage treatment. The moisture content was measured by Karl Fischer potentiometric titrator, and the HF content was analyzed by acid-base neutralization titration. Table 1 shows the change values of moisture and HF content in the electrolyte before and after treatment at 45 °C. It can be seen that the additive HQ can effectively inhibit the generation of HF in the electrolyte and improve the stability of the electrolyte.

Table 1

Example 4

Add 0.2wt% and 1.0wt% additive HQ to the 1M LiPF ₆ EC/EMC/DEC (1:1:1w) basic electrolyte, and investigate the basic electrolyte and the additive-containing electrolyte on the CHI660D electrochemical workstation. The results of linear sweep anchor voltammetry are shown in Figure 3. It can be seen that the use of HQ additives in conventional carbonate-based LiPF _6- based electrolytes can effectively increase the electrochemical window of the electrolyte, improve the oxidation resistance of the electrolyte, and effectively increase the decomposition potential of the conventional electrolyte to 5.0V. 1M LiPF ₆ EC/EMC/DMC ( ₁ :1 _{: 1w} ) electrolyte and 1M LiPF ₆ EC/EMC/DMC (1:1:1w)+ The effect of 0.5wt% HQ electrolyte on the cycle performance of the battery, the results show that after 100 cycles of charge and discharge at a rate of 0.2C, the battery capacity retention rate of the electrolyte without the additive HQ is 82%, while the battery with the additive is The capacity retention after 100 cycles was 91%. It can be seen that the LiNi _0.5 Mn _1.5 O ₄ //Li half-cell experiment further verifies that the additive HQ can improve the oxidation stability of the electrolyte.

Example 5

Mix graphite, acetylene black conductive agent and CMC binder in the ratio of 93.2:2.5:4.3 to make negative electrode slurry, and evenly coat it on the copper foil to make the negative electrode sheet, in the ratio of 91:4:5 in NMP Mix LiFePO ₄ , conductive graphite and PVdF binder to make a positive electrode slurry, and evenly coat it on an aluminum foil to make a positive electrode sheet. Combined with Celgard 2325 polymer separator, the positive electrode sheet, separator and negative electrode sheet are wound to make a 10Ah square aluminum shell cell. The above-mentioned 10Ah batteries were charged and discharged on the battery charging and discharging instrument. The electrolyte of 1M LiPF ₆ EC/EMC/DEC/VC/1,3-PS (1:1:1:0.1:0.3 mass ratio) containing 0.2wt% additive HQ was selected to investigate the cycle performance of the cell at room temperature, and the results It shows that the capacity retention rate is 85% after 1500 charge-discharge cycles at a rate of 0.5C, which is equivalent to the electrolyte without additive HQ. It is believed that HQ does not affect the normal temperature cycle performance of the battery. Figure 4 is a cell using two electrolytes of 1M LiPF ₆ EC/EMC/DEC/VC/1,3-PS (1:1:1:0.1:0.3 mass ratio) with and without 0.2wt% additive HQ Under the high temperature condition of 60°C and the cycle data of 0.5C charge-discharge rate, the capacity retention rate of the battery using the additive HQ is as high as 84% after 250 cycles, while the capacity retention rate of the battery without the additive HQ is only 250 cycles after 250 cycles. was 72%. It can be seen that the use of additive HQ can effectively improve the high temperature cycle performance of the battery.

The above embodiment is a preferred embodiment of the present invention, but the embodiment of the present invention is not limited by the above embodiment, and any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention , all should be equivalent replacement methods, and are all included in the protection scope of the present invention.

Claims (2)

1. functional additive that is used for non-aqueous electrolyte for lithium ion cell is characterized in that: its consumption is equivalent to the 0.01-5 % that carbonate solvent and lithium salts are formed electrolyte quality, and described additive is an oxine.

2. functional additive according to claim 1 is characterized in that: described additive amount is the 0.05-1.5 % of carbonates electrolyte quality.

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